Due to environmental concerns pertaining to the use of fossil fuels in connection with generating electric power, including the non-renewability of such fossil fuels and carbon emissions and other pollutants generated when fossil fuels are burned, an increasing amount of research and funding has been directed towards systems that utilize renewable energy sources to generate electric power. These systems include solar power plants, wind turbines, geothermal power systems, and the like. An exemplary solar power system is a solar power tower (which can also be referred to as a central tower power plant, a heliostat power plant, or a power tower). A solar power tower utilizes an elevated central receiver to collect focused solar radiation from a plurality of reflectors (also referred to as collectors), such as heliostats. Solar radiation is reflected from the reflectors and concentrated at the central receiver, where a fluid is heated. The heating of the fluid can cause a turbine to be driven to generate electric power. Problems can arise, however, when the concentrated solar radiation is not relatively uniformly distributed across the surface of the central receiver. For instance, “hot spots” are undesirable on the surface of the central receiver, as damage to the central receiver may occur if too much solar radiation is concentrated at any one portion of the central receiver.
Several techniques have been developed that are utilized to measure irradiance on the surface of a central receiver of a solar power tower. An exemplary conventional method requires the use of a water-cooled flux gauge or calorimeter (a sensor) that is affixed to the surface of the central receiver. This sensor is employed to obtain a measurement of irradiance at the location of the sensor. An electronic image of the surface of the central receiver can then be captured, and intensity values of pixels of the image can be calibrated based at least in part upon irradiance measured by the sensor. This approach, however, requires the utilization of the aforementioned sensor, which can be relatively expensive and difficult to calibrate.
Another conventional approach utilizes a CCD camera to measure the irradiance distribution on the surface of the receiver from a dish concentrator. Instead of using a flux gauge or calorimeter, however, the total power from the dish collector is calculated and utilized to calibrate pixel values of an image captured by way of the CCD camera. This approach requires that an entirety of a beam is captured by the receiver. In operation, a solar power tower can be surrounded by hundreds or thousands of reflectors—therefore, it is impractical to expect no spillage of concentrated light outside of the surface area of the central receiver.
Yet another exemplary conventional approach for computing an irradiance distribution across the surface of a central receiver is the utilization of a flux scanner that can measure their radiance distribution from an entire heliostat field. A flux scanner comprises flux sensors that are included in a long wand that is configured to rotate in front of the central receiver. A remote video camera is used to capture images of the reflected irradiance from the wand as such wand is rotated, and the sensors in the wand are used to calibrate pixel values corresponding to the Lambertian surface of the wand. The resulting recorded images of the wand while rotated in front of the receiver are stitched together to yield a flux map of the irradiance distribution at the aperture of the central receiver line.
Yet another exemplary conventional approach for determining irradiance distribution across the surface of a central receiver of a solar power tower includes the use of a flux measurement system that comprises an infrared camera that measures the surface temperature of the central receiver, and the irradiance distribution across such receiver can be inferred based upon the surface temperature. Utilizing this approach, many processes and parameters must be known to calculate the irradiance distribution across the surface of the central receiver. These include the thermodynamic properties of the fluid that is to be heated, properties of the materials of the central receiver, and heat loss due to radiation and convection. Uncertainty in these parameters and processes and associated parameters that impact these processes, such as ambient temperature and wind speed, can contribute to uncertainties in the calculated irradiance distribution.
Furthermore, as mentioned above, solar receivers are generally surrounded by numerous reflectors (heliostats, mirrored troughs, or dish concentrator facets). From certain perspectives, this reflection of solar radiation can result in an unintended side effect: solar glare. Assessment of the potential hazards of glint and glare from concentrating solar power plants is an important requirement to ensure public safety. Glint can be defined herein as a momentary flash of light, while glare is defined as a more continuous source of excessive brightness relative to the ambient lighting. There is currently no cost effective solution in place to obtain a measure of glint or glare caused by reflectors, receivers, or other components utilized in concentrating solar power systems such as power tower systems, linear concentrator systems (e.g., parabolic troughs or linear Fresnel) and dish/engine systems.